Enhanced Damage Tolerance of Out-of-Autoclave Composites Through Multi-Scale Interlaminar Toughening

Out-of-autoclave (OoA) processing offers a more energy-efficient and scalable route for composite manufacturing, aligning with the goals of green aviation. However, OoA composites typically exhibit poor interlaminar fracture toughness, limiting their use in demanding structural applications. This study proposes a multi-scale interlaminar toughening strategy to enhance the damage tolerance of carbon fibre/epoxy composites produced via OoA methods. The approach combines micro-scale thermoplastic veils and nano-scale core–shell rubber (CSR) particles within the interlaminar regions to synergistically improve fracture performance. Mode I and Mode II interlaminar fracture performance were evaluated using double cantilever beam (DCB) and four-point end-notch-flexure (4-ENF) tests, respectively. Low-velocity impact tests were also conducted to assess damage resistance under dynamic loading. The results reveal substantial improvements in both fracture energies and impact resistance with hybrid multi-scale toughening. Specifically, the combined toughening strategy achieved a 275% increase in Mode I fracture energies and a significant reduction in the damage area under impact. These findings demonstrate the effectiveness of multi-scale interlaminar toughening in addressing the limitations of OoA composites, providing a promising pathway toward lightweight, damage-tolerant structures for sustainable aerospace applications.